Mitochondrial dysfunction is an early feature of Alzheimer's disease (AD). Amyloid-? peptide (A?) has deleterious effects on mitochondrial function and contributes to respiratory chain impairment, energy failure, generation of reactive oxygen species (ROS), and neuronal apoptosis in AD. Recent studies have highlighted the pivotal role of mitochondrial A? in Alzheimer's disease pathogenesis. Cyclophilin D (CypD), a peptidylprolyl isomerase F, resides in the mitochondrial matrix and associates with the inner mitochondrial membrane during the mitochondrial membrane permeability transition (mPT). CypD plays a central role in opening the mitochondrial membrane permeability transition pore (mPTP) leading to cell death. The level of CypD was significantly elevated in neurons in AD-affected regions. We have demonstrated the presence of CypD-A? complex in the cortical mitochondria of AD brain and Tg mAPP mice, and the binding of recombinant CypD protein to A? with surface plasmon resonance (SPR). CypD deficiency (lacking A? binding partner) protected against A? -mediated mitochondrial and synaptic dysfunction. Further, our pilot studies showed that increased expression of CypD (enhancing CypD- A? interaction) exacerbated mitochondrial and neuronal perturbation as well as early onset of deficits in spatial learning/memory. These studies lead us to hypothesize that CypD is a critical mitochondrial target potentiating A?-mediated mitochondrial and neuronal dysfunction. Blockade of the CypD-A? interaction will attenuate A?-induced mitochondrial and neuronal perturbation. The goal of this project is to elucidate the basis of CypD-A? interaction using crystal (Aim 1) and NMR (Aim 2) structural analyses, and to analyze critical aspects of the intracellular pathway through which engagement of CypD with A? induces mitochondrial and neuronal dysfunction (Aim 3). The proposed research is highly significant and innovative on three points. First, the expected outcomes will reveal the structural details of CypD with A? at atomic resolution, which has never been reported. Second, the consequence of CypD-A? interaction in A?-mediated mitochondrial and neuronal dysfunction will be elucidated based on structural and functional analysis. Third, the results of this proposal will have a profound impact on the AD field by establishing a new target for preventive and therapeutic intervention. PUBLIC HEALTH RELEVANCE: The goal of this project is to elucidate the basis of CypD-A? interaction using crystal and NMR structural analyses, and to analyze critical aspects of the mitochondrial pathway through which engagement of CypD with A? induces mitochondrial and neuronal damages. The results of this proposal will have a profound impact on the AD field by establishing a new target for preventive and therapeutic intervention.